Patient- and Ward-Specific Risk Factors for Intensive Care Unit Readmission and Implications for Patient Outcomes: A Scoping Review

Background: Unplanned ICU readmissions are associated with adverse outcomes, including mortality. However, evidence on risk factors for readmission remains inconclusive. This scoping review was conducted to summarize risk factors for unplanned ICU readmission and their association with mortality. Methods: Following PRISMA-ScR guidelines, PubMed and Web of Science were systematically searched up to April 21, 2026, without restrictions on language, country, or publication date. We included observational studies and systematic reviews with meta-analyses investigating risk factors for ICU readmission in adults. Data on study characteristics, readmission rates, mortality, and patient- and ward-related risk factors were extracted and summarized. The quality of the studies was assessed using the Newcastle–Ottawa Scale and AMSTAR 2. Results: A total of 119 observational studies and two meta-analyses were included. There was substantial heterogeneity in patient populations, specialties, study duration, and follow-up periods. Readmission rates ranged from 0.8% to 34.9%. ICU readmission was consistently associated with higher mortality. The most consistent patient-related risk factors were advanced age, a higher number of comorbidities, greater illness severity, organ support, and longer initial ICU stay. Among ward-related factors, nighttime discharge was the most consistently reported. Most observational studies achieved high scores on the Newcastle–Ottawa Scale (8 or 9 points). However, this evaluation should be viewed with caution, given the predsominance of retrospective studies. Conclusions: ICU readmission is a multifactorial event influenced by patient- and ward-related factors. Key predictors include advanced age, comorbidities, prolonged organ support, and greater illness severity. Nighttime discharge was the most consistent modifiable organizational risk factor. Discharge decisions should incorporate comprehensive clinical assessment, structured planning, and appropriate post-ICU care. Future multicenter prospective studies using standardized definitions are needed to improve risk prediction and support evidence-based discharge strategies.